The present invention relates to a fuel system, particularly adapted for boats, and comprises a releasable coupling for connecting a tube or hose between the fuel tank and the engine, the coupling comprising a fuel valve adapted to open and close automatically when the coupling parts are respectively connected and disconnected.
For smaller boats a fuel system is commonly used in which a fuel hose between the fuel tank and the engine can be disconnected when the boat is not in use. Such systems are particularly used for boats having an outboard engine and a fuel tank separate from the engine. These fuel tanks are usually not permanently installed, but are portable, so that the user of the boat may bring the tank along when leaving the boat, or put the tank into, for example, a closeable compartment on board the boat.
The hose being used to connect the tank and the engine is usually adapted to be disconnected from both the tank and the engine, and is always adapted to be disconnected from at least one of them. The coupling used in the system, at one or both ends of the hose, is usually a quick coupling which comprises a fuel valve adapted to open automatically when the coupling parts are brought together. The fuel valve, which is usually situated in the coupling part mounted on the tank and/or the engine, may comprise a spring biassed valve element, and the coupling part or parts mounted on the hose may comprise a hollow stud in communication with the hose. When the cooperating coupling parts are connected, the hollow stud urges the valve element to an open position, and the spring urges the valve element to a closing position when the coupling part on the hose is removed.
In order to prevent the coupling parts from being unintentionally disconnected the couplings are usually equipped with a retaining hook or the like, which must be released by hand before the coupling parts can be pulled apart.
To prevent the development of an increasing sub-atmospheric pressure inside the tank caused by the suction of fuel to the engine, the couplings usually comprise a vacuum valve. This valve is a one-way valve, for example, a valve element which is biassed towards a valve seat by a spring. Thus, the valve will open for inlet of air into the tank when the sub-atmospheric pressure has reached a predetermined value, but will mainly be closed when the vacuum is less than such value and when there is a pressure above the atmospheric pressure inside the tank.
The above prior art systems show discrepancies which constitute a danger. Experiences show that during storage of such fuel tanks, large pressures are also developed in the tanks, especially when they are kept in warm places. This fact does not itself constitute a disadvantage, because the tanks are adapted to withstand considerable pressures, and from a safety standpoint interior pressure above atmospheric is more desirable than letting fuel vapour escape at the storage location, which would thus increase the risk of explosion and fire.
However, the danger due to the pressure inside the tank is brought about when the hose is connected to the tank after the tank has been brought on board the boat. The pressure head inside the tank increases the possibility of leakages from the coupling itself, the hose or the vacuum valve. In particular when the couplings are worn there will be insufficient sealing between the coupling part on the tank and/or on the engine and the coupling part or parts on the hose. The pressure may cause the fuel to leak into the boat. Also the hose may be unable to withstand the pressure, and the fuel may escape through fissures. A particularly weak point is the bladder which is normally situated on the hose, for the purpose of pumping fuel to the engine prior to starting such as when there is only a small pressure head inside the tank. Moreover, the vacuum valves in the prior art couplings have shown to produce fuel leakages. The passage in which the vacuum valve is situated opens in the vicinity of the tank, and fuel vapour incidentally leaking through the vacuum valve because of the pressure head will accumulate inside the boat.
In the above manner a large quantity of fuel, in the form of liquid or vapour, may escape from the fuel system and accumulate in the boat, and may give rise to an explosion and fire. Experience has shown that this happens, and the prior art systems are thus not safe in this respect.